1. Field of the Invention
This invention relates to improving the state of the art of locating the area of contact between two surfaces moving in relation to each other. The invention also relates to improving boundary line officiating in games, such as tennis, and to characterizing the speed of impact of a projectile such as a tennis ball hitting a tennis court.
2. Prior Art
Many games, such as tennis, depend on proper boundary line officiating; however, often boundary line calls are difficult to make. In tennis, line calls are made continually as to whether a ball has landed in bounds, on a line, or out of bounds. In tennis a ball can reach velocities of 100 miles per hour or greater, which makes it very difficult for the human eye to place the area of contact on the court. Fast moving balls usually have a low aspect angle and often the ball skids on the court before bouncing up from the court, all in a very short time interval. Locating the area of contact of the tennis ball with the court with accuracy is a constant point of controversy in tennis.
In the prior art there are a number of patents that have addressed the problem of improving the state of the art of boundary line officiating. For example, U.S. Pat. No. 5,059,944 to Carmona uses an optical system for detecting and signaling an out-of-bounds ball. In that invention, optical sensor units consisting of emitter and receptor units are configured around the court and an out-of-bounds ball is signaled by an audiovisual device. There are other versions of optical sensor systems for boundary line officiating, including Wilson, U.S. Pat. No. 4,422,647, that use light beams.
There are a number of devices that use electrical/electronic sensors for improving boundary line officiating. For example, U.S. Pat. No. 4,840,377 to Bowser uses sensors that contain piezoelectric film conductors that are placed along boundary lines. On the impact of a ball the piezoelectric film creates a voltage, which is sent to a controller that communicates to a line judge whether a ball has struck a boundary line. Other devices using electrical sensors include: Harrop U.S. Pat. No. 4,855,711 that uses sensors that when compressed generate an electrical impulse; Gray U.S. Pat. No. 4,664,376 in which the ball is modified to have metal material in it so that electromagnetic fields placed in the court are disturbed when the ball is nearby thereby sensing the location of the contact; Supran U.S. Pat. No. 4,432,058 that uses an electrically conductive tennis ball which makes and breaks electrical circuits when bouncing on them; Berger U.S. Pat. No. 5,082,263 that has a tennis ball with a radar reflecting element that is then tracked with a radar; Van Auken U.S. Pat. No. 4,859,986 that has in and out of bounds circuits which can be completed by the touchdown of a conductive game ball; and Levine U.S. Pat. No. 4,365,805 that has a plurality of laminated, pressure sensitive contact type switches that are closed by pressure of a ball or foot impact.
All of these sensors have in common that the ball contact with the surface of the court is sensed or tracked and then remotely signaled to an official who then calls the play based on a combination of what he saw visually and what the sensor indicates. The official has additional information, but unfortunately there is still room for ambiguity, so calls will still be in controversy in these systems.
Thermochromic liquid crystals have been used in the prior art for temperature indication/measurement, medical thermography, nondestructive testing, radiation detectors, and for aesthetics. In the area temperature indication/measurement the uses include digital thermometers and heat warning indicators. In the area of medical thermography one use is for breast cancer detection. In the area of nondestructive testing one example is fault detection in electronic components. In the area of radiation detectors the uses include thermal imaging. Aestetic uses include advertising, decoration, jewellery, badges, fabrics and clothing. None of the prior art uses thermochromic liquid crystals to locate an area of contact.
What is needed is a sensor that indicates the area of contact of an object, such as a tennis ball, with a surface, such as a court, directly on the surface at the area of contact, as opposed to some remote signaling device. With this type of system, the players and the officials could all "see" the area of contact. The audience could also "see" the area of contact, possibly via television. Whether the area of contact is in or out of bounds, having a sensor that indicates directly where on the court the area of contact occurred would greatly increase the reality of the line calls and the "participation" in line calls, which would make the line calls better and improve the game for all parties involved. Such a system would remove the mystery of remote sensors and avoid some of their disadvantages which include modified balls that would change the game, expensive equipment that must be installed at each court, and the associated training to use the equipment and maintain it.
Another feature that is needed is to be able to characterize the speed of the impact of a projectile. In tennis this could be used to characterize the speed of a serve, for example. The prior art generally does not address this aspect; however, the devices that use radar could measure speed, but radar by its nature emits dangerous radiation. A method to characterize speed without such dangers would be a significant improvement.